Video transcript

In this video, I want to
talk about ependymal cells. But to do so, first let me draw
the brain and the spinal cord. So I'll just draw a big
circle for the brain and I'll draw a long structure
like this for the spinal cord. Because there are
spaces inside the brain and inside the spinal cord
that are full of fluid. And these spaces are
connected together. And they are connected
to this little skinny canal that goes down
the spinal cord. And don't worry about
the anatomy of this. We'll go into this in more
detail in other videos. But these spaces
are full of a kind of fluid called
cerebral spinal fluid for the brain and
the spinal cord. And the lining of these
spaces is called the ependyma, which is made up
of ependymal cells. The ependyma is named for
a Greek word for covering. And the ependymal cells
that make up the ependyma are glial cells of the
central nervous system derived from neural stem cells. If we zoom in here and look at
some of these ependymal cells, we'll see that they form a
simple, cuboidal epithelium. Simple, meaning that they're
just one layer of cells; cuboidal, meaning
that they're shaped like little cubes;
and epithelium, meaning they're a
covering, in this case the lining of a cavity. So let's say that this
is the side facing the cerebral spinal
fluid, which I'll just write as "CSF" for short,
for Cerebral Spinal Fluid. And that this side faces
the interstitial fluid of the central nervous system,
all the fluid between the cells of the brain and
the spinal cord. And I'll just write "IF" as
short for Interstitial Fluid. On the side of the
ependymal cells facing the cerebral
spinal fluid are a large number of little tiny
processes called microvili, that increase the surface
area of the ependymal cells on that side. They also have some processes
that are a little longer, called cilia, that are these
mobile, whip-like structures that kind of whip
around and help move the cerebral
spinal fluid around. One of the main functions
of ependymal cells is to form a barrier between
the cerebral spinal fluid and the interstitial fluid. So to some extent, they
limit the movement of cells and large molecules between
these fluid-filled spaces and the interstitial fluid
of the tissue itself. Now as barriers go,
the ependymal cells form a fairly leaky
barrier, particularly if we were to compare it to
the blood-brain barrier created by the capillaries in the
central nervous system and the astrocyte end-feet. And the fact that this is
a relatively leaky barrier is actually useful
for medical purposes because there are
areas where we can sample the cerebral spinal fluid
and send it to the laboratory. And when we analyze the
cerebral spinal fluid, we can often get a
lot of information about what's happening in
the tissue of the brain and the spinal cord because
it's a relatively leaky barrier. The second major function
of ependymal cells is to participate in secretion
of the cerebral spinal fluid. So secreting CSF,
cerebral spinal fluid. Specialized ependymal cells and
capillaries form little tufts in some of these
spaces in the brain. And this is actually where
the cerebral spinal fluid is secreted into these
spaces, so that there will be capillaries very
close to the ependymal cells. And in these little
tufts, fluid will be secreted across
the ependymal cells to create the
cerebral spinal fluid.